-LRB- CNN -RRB- -- Rory McIlroy was confirmed as winner of the Race to Dubai Sunday despite not lifting a club in anger for six weeks .

Victory for American Brooks Koepka in the Turkish Airlines Open -- at the expense of McIlroy 's nearest challengers Marcel Siem , Jamie Donaldson and Sergio Garcia -- left the Northern Irishman with an unassailable lead ahead of the DP World Tour Championships in Dubai later this week .

It is the second time in three years that McIlroy has ended the season as European number one , having claimed two major titles and a lucrative World Golf Championship event .

But eyebrows were raised when the 25-year-old McIlroy said he would sit out the WGC-HSBC Champions and BMW Masters tournaments in China to prepare for a court battle against his former management company .

With such a big lead after his earlier triumphs , the world number one judged he afford to miss out on more big pay days , his last appearance on the European Tour coming with a second place at the Alfred Dunhill Links Championship in the first week of October .

Germany 's Siem , who won the BMW Masters event , made a brave attempt to win in Turkey to keep the race alive .

He started the final round Sunday just a shot off the lead , but could only card a closing 71 to finish tied eighth , with Donaldson 19th and Garcia 25th .

Koepka , who lives in Florida , clinched his first European Tour victory with a superb closing 65 on the Montgomerie Maxx Royal course at Antalya to finish 17 under par .

It left him a shot clear of England 's Ian Poulter , who was left to rue a missed six-foot birdie putt on the 18th to force a playoff .

Henrik Stenson of Sweden finished third to move into second in the Race to Dubai standings , but 2,726,514 points behind McIlroy , with 1,666,600 on offer to the winner in Dubai next Sunday .

McIlroy will go in search of a search of a second win in three years at Jumeirah Golf Estates , delighted to have wrapped up the Harry Vardon Trophy , awarded to the player who finishes the season as Europe 's top player .

`` This has obviously been the best season of my career by a long way , and to win the Race to Dubai for the second time really is something truly special , '' he told the official European Tour website .

`` That four-week spell over the summer , from the British Open to the US PGA Championship , would have to be the best golf of my life , so I feel like I 've really earned the Race to Dubai . ''

The top 60 players in the Race to Dubai after this week 's tournament , with Koepka up to sixth , will play in the $ 8 million end of season finale .

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Brooks Koepka wins Turkish Open title

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Holds off Ian Poulter by a shot at Antalya

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Rory McIlroy confirmed as winner of Race to Dubai

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McIlroy 's main challengers needed to win in Turkey to prolong race